1. Field of the Invention
This invention relates to a control apparatus which can measure the electrical constant of an AC rotary machine such as induction machine or synchronous machine, and a method for measuring the electrical constant.
2. Description of the Background Art
Heretofore, there has been introduced a method which uses a control apparatus for an AC rotary machine and which measures, for example, an armature inductance or a magnetic flux vector as the electrical constant of the AC rotary machine.
By way of example, a control apparatus in Patent Document 1 (Japanese Patent No. 3,019,653) first executes constant-V/f control processing and outputs a primary voltage command V1c in proportion to a primary angular frequency command ω1. Besides, the control apparatus integrates the primary angular frequency command ω1 so as to evaluate the phase command θv1 of a primary voltage vector. In addition, the control apparatus outputs a PWM signal in correspondence with the magnitude command V1c of a primary voltage and the phase command θv1 of the primary voltage vector, thereby to perform a steady running with a rated magnetic flux (the ratio between a rated frequency and a rated voltage) near the rated frequency. Subsequently, the control apparatus executes predetermined calculations by general three-phase AC/two-phase DC conversion processing, thereby to evaluate a reactive power component current Id and an active power component current Iq. In addition, the control apparatus evaluates a self-inductance, namely, the armature inductance L1 by a predetermined calculation on the basis of the currents Id and Iq, the primary angular frequency command ω1 and the primary voltage command value V1c, and a primary resistance r1 and a resultant leakage inductance Lx (Lx≈11+12) which have been measured beforehand.
Besides, Patent Document 2 (JP-A-2002-171797) discloses a system including a power converter which feeds power to a synchronous motor of permanent magnet type, and a control apparatus which controls the output voltage of the power converter with the magnitude of the magnetic flux vector of the permanent magnet of the synchronous motor. In addition, the control apparatus includes magnetic flux measurement means configured of a magnetic flux measuring current controller which has an acceleration mode wherein the synchronous motor is rotated to a predetermined revolution number by causing an AC current of predetermined magnitude to flow through the synchronous motor, and a measurement mode wherein the primary current of the synchronous motor is set at zero or a minute value, a magnetic flux measuring magnetic flux vector calculator which calculates a magnetic flux vector by temporally integrating the primary voltage vector of the synchronous motor detected or estimated, when the magnetic flux measuring current controller is in the measurement mode, a magnetic flux calculator which evaluates the magnitude of the magnetic flux vector from the output of the magnetic flux measuring magnetic flux vector calculator, and a magnetic flux memory which stores the output of the magnetic flux calculator therein. Further, the control apparatus operates the magnetic flux measurement means in a case where the magnitude of the magnetic flux vector stored in the magnetic flux memory needs to be updated.
In the prior-art control apparatus for the AC rotary machine as is disclosed in Patent Document 1, an inverter is driven on the basis of the primary angular frequency command value ω1 and the primary voltage command value V1c, so as to run the AC motor in a steady state, and the component Iq in the same direction as the inverter primary voltage vector direction of a motor current vector I1 and the component Id in the same direction as a direction lagging 90° from the same direction as the inverter primary voltage vector direction are calculated from the phase with the primary angular frequency command integrated and the current detection value of the AC motor on this occasion. In addition, the control apparatus calculates the primary self-inductance L1 or mutual inductance M of the AC motor by employing only the four fundamental arithmetic operations of a voltage, the currents and an angular frequency on the basis of the primary angular frequency command value ω1 and the primary voltage command value V1c or a primary voltage detection value V1, and the currents Iq and Id. Therefore, the control apparatus has the problem that noise which exists in the voltage detection value or the current detection value is directly reflected upon a calculated value. Another problem is that the measured constant is also influenced by the noise. Still another problem is that, since the measurement of the armature inductance is performed by the predetermined calculation based on the primary resistance r1 and the resultant leakage inductance Lx (Lx≈11+12) measured beforehand, the measurement precision of the armature inductance degrades unless the precisions of the primary resistance r1 and the resultant leakage inductance Lx measured beforehand are good.
On the other hand, the control apparatus for the AC rotary machine as is disclosed in Patent Document 2 employs the magnetic flux measuring magnetic flux vector calculator which calculates the magnetic flux vector by temporally integrating the detected or estimated primary voltage vector of the synchronous motor. In case of measuring the magnitude of the magnetic flux vector of the permanent magnet, accordingly, the control apparatus evaluates the magnitude of the magnetic flux vector of the permanent magnet from the length of a radius, with respect to that output of the magnetic flux measuring magnetic flux vector calculator which indicates the magnetic flux vector depicting a circular locus. Therefore, the control apparatus has the problems that the amplitude of a magnetic flux cannot be measured as a DC quantity, and that the evaluation of the length of the radius of the magnetic flux vector cannot be realized by an inexpensive arithmetic unit because it requires a microcomputer or the like arithmetic unit capable of sufficiently fast sampling.